This invention relates generally to systems for the passive restraint of vehicle occupants and, more particularly, to an arrangement for inflatable restraint systems resulting in improved air bag deployment geometry, particularly with inflators having non-symmetric gas output.
Safety restraint systems which self-actuate from an undeployed to a deployed state without the need for intervention by the operator, i.e., "passive restraint systems", and particularly those restraint systems incorporating inflatable bags or cushions, as well as the use of such systems in motor vehicles have gained general appreciation.
It is well known to protect a vehicle occupant using a cushion or bag that is inflated with gas, e.g., an "air bag", when the vehicle encounters sudden deceleration, such as in a collision. During deployment, the rapidly evolving gas with which the bag is typically filled is an inert gas, e.g., nitrogen. In such systems, the air bag is normally housed in an uninflated and folded condition to minimize space requirements. In an emergency, gas is discharged from an inflator to rapidly inflate the air bag. The air bag, upon inflation, serves to restrain the movement of the vehicle occupant as the collision proceeds. In general, such air bags are commonly designed to be inflated in no more than a few milliseconds.
Vehicular inflatable restraint systems generally include multiple crash sensors generally positioned about or mounted to the frame and/or body of the subject vehicle and serve to sense sudden decelerations by the vehicle. In turn, the sensor sends a signal to an air bag module or assembly strategically positioned within the riding compartment of the vehicle to actuate deployment of the air bag. In general, an air bag provided for the protection of a vehicle driver, i.e., a driver side air bag, is mounted in a storage compartment located in the steering column of the vehicle. Whereas, an air bag for the protection of a front seat passenger, i.e., a passenger side air bag, is typically mounted in the instrument panel/dash board of the vehicle.
Typical air bag restraint systems make use of an air bag module which generally includes an outer reaction housing or canister, commonly referred to as a "reaction can" or, more briefly, as a "can". The reaction canister generally serves to support or contain other components of the air bag module system, including what is referred to as a "air bag inflator" or, more briefly, as an "inflator", or, alternatively, as a "generator". The inflator, upon actuation, acts to provide the gas to inflate the air bag.
Inflators used in such systems are typically either of a pyrotechnic or hybrid type.
Pyrotechnic inflators generally contain a gas generating material which, upon activation, generates gas used to inflate the air bag. In general, the inflation gas produced by a pyrotechnic inflator is emitted from openings or emission ports along the length of the inflator.
In contrast, hybrid inflators in addition to a body of ignitable pyrotechnic material generally contain as the primary inflation gas a stored, compressed gas which, upon proper actuation, is expelled from the inflator. As a consequence of the physics associated with the storage of compressed gases, the container used to store this compressed gas typically has a cylindrical shape. Furthermore, the discharge of gas from such a cylindrically shaped gas storage container typically occurs by way of openings or emission ports at only one end of the cylindrical container.
It is generally desired that the air bag attain straight or a non-skewed geometry upon deployment, particularly where the air bag module assembly is for installation mid-mount within a vehicle dashboard or panel, that is in a central region of the vehicle dashboard or panel, between the upper and lower portions thereof and for which the direction of the bag deployment towards the vehicle occupant is generally perpendicular. Such an installation is commonly referred to as a "mid-mount installation."
To that end, it is generally desired that the emission of gas into the air bag from such a storage container be done in a fairly uniform manner. With typical air bag/inflator assemblies, such uniform emission is generally attained by having a relatively even emission of gas into the deploying bag along the length of the gas inlet opening of the air bag connected, directly or indirectly, to the inflator. In this way the bag is properly uniformly deployed and the risk of the bag deploying in a skewed manner due to the discharge of gas from only one end of the storage container is avoided.
With inflators which discharge or emit inflation gas relatively evenly from openings along the length of the inflator, such as the above-described pyrotechnic inflators, such non-skewed air bag deployment commonly results. However, with inflators which produce a non-symmetric gas output, such as the above-described hybrid inflators, wherein gas discharge is typically by way of openings or emission ports at only one end of a cylindrical container, means for avoiding skewed deployment of the air bag must be provided.
One approach that can be employed towards attaining such desired straight or non-skewed air bag deployment geometry is to employ a diffuser device having a relatively low gas flow through area. That is, the diffuser largely restricts the gas flow therethrough such that the inflation gas which does pass therethrough flows generally perpendicular to the face member portion of the diffuser. Unfortunately, as a result of inflation gas flow restriction, such an approach can result in unacceptable slowing of the air bag deployment process.
Another approach that can be employed towards attaining such desired straight or non-skewed air bag deployment geometry is to employ a diffuser device incorporating one or more baffle surfaces in order to control or redirect gas flow. While the use of such baffle surface-including diffusers can be at least marginally helpful in reducing the skewness of an air bag upon deployment, the incorporation of such baffles typically increases not only production complexity but also the costs associated with such production.
Thus, a simple, low cost means of reducing or eliminating the risk of skewed air bag deployment without significant gas flow restriction, particularly in those assemblies employing inflators which produce a non-symmetric gas output, is desired.
Further, upon inflation and deployment of the air bag, the reaction housing canister acts to absorb or retransmit the resulting air bag deployment forces to the vehicle. The reaction housing typically is an open-mouthed container into which the air bag, in an uninflated and folded condition, is also placed. In prior art devices the air bag is commonly attached either about the inflator or to the reaction housing itself. As a consequence of such attachment, the reaction housing is especially susceptible to deformation as a result of the forces produced during and associated with bag deployment. For example, when the air bag is inflated the peripheral portion of the opening of the air bag is typically pushed outwardly with respect to the housing oftentimes resulting in deformation of the housing. By virtue of the open-mouth shape or form generally taken by these reaction housings such deformation is generally referred to as "bell-mouthing".
In order to resist such deformation and to prevent the peripheral portion of the gas inlet opening of the air bag from moving outwardly with respect to the housing, conventional air bag devices have adopted various measures.
In practice, bell-mouthing can be reduced or limited by fabricating the reaction housing using a metal of greater thickness and/or strength. Such use of a thicker metal, however, can result in a significant and detrimental increase in the overall weight of the housing. Of course, weight minimization is an especially important concern in modern vehicle design as a result of the impact the weight of a vehicle has on vehicular fuel mileage. The alternative of fabricating the reaction housing using a stronger type of material of construction is not always practical as stronger materials of construction generally have higher material costs associated with them and would thus increase the cost associated with such safety restraint systems.
Commonly assigned U.S. Pat. No. 4,941,678, Lauritzen et al., issued Jul. 17, 1990, discloses a lightweight housing canister assembly having a design avoiding such bell-mouthing. The assembly includes a tether strap, at the mouth inside the bag, that restricts the loading of the reaction canister and positioned transversely thereto. This tether strap retains the spreading forces at the mouth of the canister upon bag deployment. This allows the use of a lighter section at the mouth of the canister and eliminates the need for reinforcing flanges along the sides of the canister, which flanges would undesirably increase the weight of the assembly. For retaining the bag in the assembly, the patent discloses that notches formed on the inner side of each of the walls of the reaction canister body form a bag retaining ring shelf for retaining a continuous attachment ring formed at the gas inlet opening of the inflatable bag.
In the past, various vehicular safety restraint inflatable cushion designs have employed thin strips of material (referred to as "tethers") which are attached to opposed internal sides of the cushion. Such tethers serve to limit the extension of the cushion upon deployment. Thus, whereas an untethered driver side air bag will typically extend about 15 to 20 inches towards the driver, a tethered air bag will only typically extend about 10 to 13 inches towards the driver.
U.S. Pat. No. 5,131,680 discloses a type of hybrid inflator and includes a diffuser. The disclosed inflator assembly includes a generally cylindrical container, a generally cylindrical diffuser, and a manifold assembly, secured to one end of the container. The diffuser is larger in diameter than the container and is mounted to encircle both the container and the manifold assembly. Further, the diffuser, which has openings through which the gas is directed to the air bag, extends substantially the entire length of the manifold assembly and a significant portion of the length of the container. Because this diffuser encircles both the container and the manifold assembly and must be able to withstand the stresses applied thereto during operation, such diffusers are generally more bulky and weighty than would be preferred.
In addition, there are a number of U.S. patents that at least in part relate to air bag retention and/or conveyance of the inflating gas into the air bag.
For example, U.S. Pat. No. 4,986,569 discloses an air bag attachment system comprising a canister having a shoulder on a peripheral edge flange for seating of a metal rod disposed in a channel in the air bag. The edge flange of the canister is reentrantly folded about the rod to retain the air bag on the canister.
U.S. Pat. No. 5,069,480 discloses an air bag retainer assembly which includes a pillow or air bag assembly including a pillow retainer to which is attached an inflatable pillow or air bag and which retainer is secured to the reaction housing assembly. Gas, supplied by a gas generator, will flow upon activation through openings provided in the retainer and into the pillow or air bag. The air bag is attached to the retainer by means of a V-shaped hem sewn about the end of the bag. Upon movement of the hem and air bag forward, the open side of the V-shaped hem engages and envelopes the circumferential edge of the retainer.
Examples of other such patents include: U.S. Pat. No. 3,708,181 which specifies the use of a nozzle through which pressure is transferred from a gas tank to an inflatable bag with the tank and nozzle joined together by way of tongue and groove joints while a continuous, flexible resilient holding member holds the edge portions of the bag in position in a groove formed around the nozzle discharge; U.S. Pat. No. 4,111,457 which discloses the use of a clamping ring to secure the edge of an air bag to the housing of the inflatable restraining device; U.S. Pat. No. 4,136,894 which discloses the use of an apertured diffuser to cover each of three independent gas generant-containing chambers of a specifically designed housing; U.S. Pat. No. 5,062,664 which specifies a hollow cylindrical member or canister having an opening into which a gas generator is inserted and having the open end of the air bag envelope the cylindrical member; and U.S. Pat. No. 5,058,919 which discloses an air bag module construction and assembly technique wherein a screen-shaped member is used to retain a folded air bag in the housing.
Nevertheless, a low weight and low cost solution to the problems of bell-mouthing and uniform gas distribution and bag deployment is still desired.
In practice, the component parts of such inflatable restraining devices, particularly the inflatable air bag and the housing, are joined and held together by means of selected fasteners such as screws, rivets or bolts. For example, a selected fastener is typically passed through fastener holes which have been preformed in the respective parts to be fastened together. Unfortunately, a problem frequently experienced in the assembly of these inflatable restraining units is difficulty in achieving and maintaining desired and proper fastener hole alignment of the respective parts to be fastened together. Also, in order to avoid undesired point loading of the stresses generated upon bag deployment, it is generally preferred to secure or fasten the bag into the assembly by means of fastening the bag between two load bearing materials (e.g., metals), such as between the reaction canister and metal retaining flanges or a metal ring placed about the bag gas inlet opening, for example. In this way, undesired loading of bag deployment stresses at or about the fastener holes in the bag fabric is reduced and preferably avoided.
In general, such fastening is done through the reaction canister itself, thereby simplifying the assembly process as the canister, bag and metal retaining flanges or metal ring are all simultaneously fastened together by means of such fastening. Unfortunately, it is difficult to simultaneously maintain proper alignment of the fastener holes in the canister, bag and retaining flange as the fastener holes in the relatively flexible bag material tend to become easily displaced relative to the fastener holes in the canister and/or retaining flange. As a result, an assembly worker must either be dedicated to maintaining the fastener holes in proper alignment or else a worker will have to stop whatever else that worker was doing in order to realign the fastener holes in the bag with the fastener holes in the canister and in the retaining flange. This of course slows and increases the cost of the assembly process. Further, a requirement for human intervention to reeffect proper fastener hole alignment prevents implementation of a more fully automated assembly process.
Thus, a relatively simple, low cost bag attachment and retaining mechanism whereby the fastener holes in the air bag are maintained in alignment with the fastener holes in adjacent members and which mechanism permits an easy adaptation to automated production and assembly is desired.
Air bag inflators commonly have associated with them an electrically actuatable igniter which upon actuation, in the case of a pyrotechnic type inflator as described above, ignites a gas generating material contained within the inflator. As the gas generating reaction is typically highly exothermic, a large amount of heat is generally produced during the gas generation process. Of course, human contact with this heat, either directly or indirectly by contact with surface(s) heated as a result of direct contact by the heat, is desirably to be avoided. Also, contact by the air bag with the hot gases by the inflator can itself cause damage to the air bag and result in the malfunctioning of the air bag. For example, in designs wherein the air bag is packed adjacent the inflator, during the short time interval immediately following the onset of actuation, the inflator can discharge gases at both such a high rate of speed and in such a fashion whereby the gases directly impinge relatively small areas of the interior surface of the air bag, and the bag itself can suffer some type of degradation such as having a hole burned through it and thereby prevent the proper functioning of the system.
Thus, a system which allows for safe air bag deployment, including the safe dissipation of heat generated during the deployment process, without harm to the occupants of the vehicle either via the cause for the deployment of the air bag, e.g., a "collision" by the vehicle, or through the bag deployment process itself, is desired.
Further, while it is known to use tethers within an air bag to limit the range of extension of the air bag upon deployment, the inclusion of such tethers can complicate the production process and increase manufacturing and production costs.
Thus, a low cost assembly improvement to effect gas flow redirection and cushion deployment, as an alternative or add-on to reliance on such tethers, is needed.
In addition, reducing the size and weight of air bag module assemblies is important to facilitate the incorporation of such assemblies in various makes and styles of vehicles without significantly detrimentally effecting either the fuel mileage or the appearance of the vehicle.
Also, assembly designs which facilitate production and which allow for unobtrusive product quality checks are important aspects in the modern competitive economic world environment.
Thus, an easy to assemble, light weight, small and relatively inexpensive air bag module assembly is desired.